1. Field of Invention
The present invention relates to an output deterioration calculating apparatus and an output deterioration calculating method adopted to calculate an output deterioration in a secondary battery capable of performing charge/discharge.
2. Description of the Related Art
Methods adopted to calculate output deterioration occurring in a secondary battery mounted in an electric car which may be a hybrid electric car in the related art include the method disclosed in Japanese Laid-Open Patent Publication No. 2000-261901. In this method in the related art, the current and the voltage are detected while driving the motor with the power stored in the secondary battery, i.e., during a discharge operation at the secondary battery, and a regression line representing the discharge characteristics of the battery is obtained by sampling the voltage value and the current value at a plurality of sampling points. The deterioration factor of the secondary battery is ascertained by calculating the internal resistance in the secondary battery manifesting as the battery deterioration is calculated through the arithmetic operation and then calculating the ratio of this internal resistance to the initial internal resistance based upon the regression line thus obtained.
However, the secondary battery output deterioration calculating method in the related art poses a risk in that the detection may be executed at sampling points at which the error attributable to the current sensor to detect the current level and the error attributable to the voltage sensor employed for detecting the voltage level are superimposed on each other. This naturally leads to a risk in that the regression line may contain an error since the regression line is obtained by sampling the voltage value and the current value at a plurality of error-containing sampling points. As the internal resistance value calculated from the regression line is different from the value of the actual internal resistance when this happens, a problem arises in that the deterioration factor cannot be accurately determined.
An object of the present invention is to provide a secondary battery output deterioration calculating apparatus and a secondary battery output deterioration calculating method that enable accurate calculation of the deterioration in the output of the secondary battery.
The secondary battery output deterioration calculating method according to the present invention adopted to calculate the battery output deterioration based upon the output ratio of the battery output measured as the secondary battery becomes depleted and the initial battery output comprises detecting an open circuit voltage of the secondary battery, detecting the voltage level as the secondary battery is charged with a constant current and calculating the output ratio in correspondence to the open circuit voltage of the secondary battery having been detected and the voltage detected as the secondary battery is charged with the constant current.
In the secondary battery output deterioration calculating apparatus according to the present invention that calculates the battery output deterioration based upon an output ratio of the battery output measured as the secondary battery becomes depleted and the initial battery output, the output ratio is calculated in correspondence to the open circuit voltage of the secondary battery and a voltage detected as the secondary battery is charged with a constant current.